| 1. |
- Afzelius, Mikael, et al.
(författare)
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Demonstration of Atomic Frequency Comb Memory for Light with Spin-Wave Storage
- 2010
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Ingår i: Physical Review Letters. - 1079-7114. ; 104:4
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Tidskriftsartikel (refereegranskat)abstract
- We present a light-storage experiment in a praseodymium-doped crystal where the light is mapped onto an inhomogeneously broadened optical transition shaped into an atomic frequency comb. After absorption of the light, the optical excitation is converted into a spin-wave excitation by a control pulse. A second control pulse reads the memory (on-demand) by reconverting the spin-wave excitation to an optical one, where the comb structure causes a photon-echo-type rephasing of the dipole moments and directional retrieval of the light. This combination of photon-echo and spin-wave storage allows us to store submicrosecond (450 ns) pulses for up to 20 mu s. The scheme has a high potential for storing multiple temporal modes in the single-photon regime, which is an important resource for future long-distance quantum communication based on quantum repeaters.
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| 2. |
- Afzelius, Mikael, et al.
(författare)
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Development of multipoint vibrational coherent anti-Stokes Raman spectroscopy for flame applications
- 2006
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Ingår i: Applied Optics. - 2155-3165. ; 45:6, s. 1177-1186
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique for coherent anti-Stokes Raman spectroscopy (CARS) measurements in multiple points is presented. In a multipass cavity the pump and Stokes laser beams are multiply reflected and refocused into a measurement volume with an adjustable number of separated points along a line. This optical arrangement was used in a vibrational CARS setup with planar BOXCARS phase-matching configuration. The CARS spectra from spatially separated points were recorded at different heights on a CCD camera. Measurements of temperature profiles were carried out in the burned gas zone of a premixed one-dimensional flame to demonstrate the applicability of this method for temperature measurements in high-temperature regions. The ability to measure in flames with strong density gradients was demonstrated by simultaneous measurements of Q-branch spectra of N-2 and CO in a Wolfhard-Parker burner flame. Interference phenomena found in multipoint spectra are discussed, and possible solutions are proposed. Merits and limitations of the technique are discussed. (c) 2006 Optical Society of America.
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| 3. |
- Afzelius, Mikael, et al.
(författare)
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Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. I. Inter-branch interference effect
- 2002
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 763-769
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Tidskriftsartikel (refereegranskat)abstract
- An improved model for pure rotational coherent anti-Stokes Raman scattering (CARS) has been developed or the dual-broadband approach. This model takes into account the fact that coherent anti-Stokes as well as Stokes radiation are generated simultaneously, and these two branches overlap and interact at high pressures giving rise to an inter-branch interference effect. In combustion studies, the anti-Stokes branch is used to determine temperature and concentrations of key species, of which nitrogen is the most widely used, and we have found that the interference effect on the anti-Stokes side is of such magnitude that it clearly needs to be taken into account at pressures of a few MPa. The necessary modifications to the total third-order susceptibility are presented and a derivation of the convolution integral for a finite-bandwidth pump source is given.
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| 4. |
- Afzelius, Mikael, et al.
(författare)
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Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. II. Rotational Raman line widths
- 2002
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 771-778
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Tidskriftsartikel (refereegranskat)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures an atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5-9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S-1-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert-Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved.
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| 5. |
- Afzelius, Mikael, et al.
(författare)
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Exact treatment of classical trajectories governed by an isotropic potential for linewidth computations
- 2004
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Ingår i: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 102:16-17, s. 1759-1765
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Tidskriftsartikel (refereegranskat)abstract
- Two models for exact classical trajectories in the field of an isotropic potential are investigated for the purpose of semiclassical linebroadening calculations. The first directly uses the exact solution of the classical equation of motion. The second starts from the equation of motion and computes the trajectory by numerical solution of the differential equations. In the framework of both models, all the computations are performed numerically, thus allowing the use of refined ab initio potential energy surfaces. For the example of the linebroadening of pure nitrogen and carbon monoxide, it is shown that, owing to the dominant short-range forces in these self-perturbed molecular systems, the limiting case corresponding to traditional parabolic trajectories can be used without any important loss of precision.
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| 6. |
- Afzelius, Mikael, et al.
(författare)
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Precision of single-shot dual-broadband rotational CARS thermometry with single-mode and multi-mode Nd : YAG lasers
- 2003
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 34:12, s. 940-945
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Konferensbidrag (refereegranskat)abstract
- The precision of single-shot coherent anti-Stokes Raman spectroscopy (CARS) thermometry is an important characteristic for the application of CARS in various combustion devices such as internal combustion engines. It is generally assumed that the precision of CARS is directly related to the spectral noise of the interacting laser fields, and previous studies have presented a theoretical model describing the behaviour of the noise as a function of various experimental parameters. In this work, the aim was to test the results predicted by the previously developed model for dual-broadband rotational CARS. We studied the precision of evaluated temperatures in pure nitrogen under different experimental conditions, namely the dependence of precision on the gas pressure and on the linewidth of the narrowband laser (the Nd: YAG laser). It was demonstrated that our experiments reproduce the main features of the model, and that a single-mode Nd: YAG laser leads to better precision than a multi-mode Nd: YAG laser for dual-broadband rotational CARS thermometry. Copyright (C) 2003 John Wiley Sons, Ltd.
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| 7. |
- Afzelius, Mikael, et al.
(författare)
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Pure rotational coherent anti-Stokes Raman spectroscopy in mixtures of CO and N-2
- 2004
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Ingår i: Applied Optics. - 2155-3165. ; 43:36, s. 6664-6672
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Tidskriftsartikel (refereegranskat)abstract
- We present a model for quantitative measurements in binary mixtures of nitrogen and carbon monoxide by the use of dual-broadband rotational coherent anti-Stokes Raman spectroscopy. The model has been compared with experimental rotational coherent anti-Stokes Raman scattering spectra recorded within the temperature range of 294-702 K. Temperatures and concentrations were evaluated by spectral fits using libraries of theoretically calculated spectra. The relative error of the temperature measurements was 1-2%, and the absolute error of the CO concentration measurements was <0.5% for temperatures less than or equal to600 K. For higher temperatures, the gas composition was not chemically stable, and we observed a conversion of CO to CO2. The influence of important spectroscopic parameters such as the anisotropic polarizability and Raman line-broadening coefficients are discussed in terms of concentration measurements. In particular, it is shown that the CO concentration measurement was more accurate if N-2-CO and CO-N-2 line-broadening coefficients were included in the calculation. The applicability of the model for quantitative flame measurements is demonstrated by measuring CO concentrations in ethylene/air flames. (C) 2004 Optical Society of America.
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| 8. |
- Afzelius, Mikael
(författare)
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Rotational Coherent Anti-Stokes Raman Spectroscopy: Experimental and Theoretical Developments in Gas-phase Thermometry
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dual-broadband pure rotational coherent anti-Stokes Raman spectroscopy was investigated in terms of thermometry and species concentration measurement for studies of combustion. The modelling of rotational CARS spectra under conditions of high pressure at room temperature was investigated. Resonant terms of the Stokes (CSRS) type were found to have a significant effect on the intensity of the anti-Stokes (CARS) branch, the effect increasing in strength with an increase in pressure. Taking account of this inter-branch interference effect improved the accuracy of temperature measurement under conditions of high pressure. An experimental study of the statistical precision of temperature measurements showed the precision to improve with use of a single-mode rather than a multi-mode Nd:YAG laser, a decrease in standard deviation by a factor of two or more being observed. Further investigation linked the measurement precision to the intensity noise observed in the CARS spectra. Temperature measurements in the post-flame zone of ethylene/air flames were conducted with the aim of studying the impact on temperature measurements of the collisional line widths employed in the model. Taking account of the line broadening of the species CO, CO2 and H2O was found to increase the evaluated temperature by 20-47 K. Spectra recorded in ethylene/air flames revealed the spectral signatures of N2, O2, CO and CO2, the spectrum of nitrogen always being strongest. The potential of rotational CARS for species concentration measurements under such conditions was also investigated. A model for binary mixtures of N2 and CO that was developed was tested for concentration measurements in these flames. The measured CO concentrations agreed closely with theoretical calculations. The collisional line broadening of Raman spectral lines in mixtures of N2 and CO was studied theoretically by means of semiclassical Robert-Bonamy calculations. The self-broadening of nitrogen (N2-N2) in particular was investigated, employing the ab initio intermolecular potential PES8. The major objective was to calculate CO-N2 and N2-CO line broadening. Use of the line widths obtained resulted in more accurate CO concentration measurements in binary mixtures of CO and N2 by use of rotational CARS.
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| 9. |
- Afzelius, Mikael, et al.
(författare)
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Semiclassical calculations of collision line broadening in Raman spectra of N-2 and CO mixtures
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:18, s. 8616-8623
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N-2 and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N-2, the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N-2 and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N-2. The central results of this work are the Q-branch linewidths of N-2-CO and CO-N-2, which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules. (C) 2004 American Institute of Physics.
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| 10. |
- Brackmann, Christian, et al.
(författare)
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Thermometry in internal combustion engines via dual-broadband rotational coherent anti-Stokes Raman spectroscopy
- 2004
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Ingår i: Measurement Science & Technology. - 0957-0233. ; 15:3, s. 13-25
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Forskningsöversikt (refereegranskat)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) has since the beginning of the 1980s been developed as a non-intrusive tool for temperature measurements in combustion. Since the introduction of the dual-broadband concept in 1986, the quality of the technique has been much improved, and application to practical combustion situations facilitated. Since the first demonstration of its use in spark-ignition engines in 1993, several measurement campaigns in engines have been accomplished. These campaigns concerned temperature measurements in the unburned gas mixture before combustion as part of a larger project with the aim of improving the knowledge on the phenomenon of engine knock. In this paper, the results of this work are reviewed with a focus on the characteristics of the technique and the quality of the evaluated temperatures. Re-evaluations of data using an improved theoretical model are presented and compared with previous results. Moreover, the treatment of large data sets on single shots from spatial regions with conditions varying from unburned to burned gas is discussed. It is demonstrated that dual-broadband rotational CARS probing nitrogen and oxygen has a high potential for thermometry at the conditions in the unburned gas mixture. Merits and limitations of the technique are discussed and the issues treated are, among others, experimental problems, data evaluation, and single-shot temperature accuracy.
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